The present invention relates to a tripod type constant velocity joint, which is disposed between rotating shafts connected at a joint angle with each other in a drive axle of, for example, an automobile, for transmitting a rotational torque.
Tripod type constant velocity joints are one of a number of types of constant velocity joints used in drive axles of, for example, automobiles.
For example, Japanese Laid Open Patent Application Nos. S63(1988)186036 and S62(1987)-233522 disclose a tripod type constant velocity joint 1, as shown in FIGS. 18 and 19(Axe2x80x94A cross sectional view of FIG. 18). This constant velocity joint 10 is provided with a hollow cylindrical housing 13 which is secured to an end of a first rotating shaft 12 serving as a drive shaft or the like on the differential gear side, and a tripod 15 which is secured to an end of a second rotating shaft 14 serving as driven shaft or the like on the wheel side. Grooves 16 are formed at three locations on the internal face of the housing 13 at an even spacing in the circumferential direction and extend outwardly in the radial direction of the housing 13 from said internal face.
On the other hand, the tripod 15 secured at one end of the second rotating shaft 14 comprises a unified form of a boss 17 for supporting the tripod 15 at one end of the second rotating shaft 14, and cylindrical trunnions 18 extending radially from three locations at equal spacing around the boss 17 in the circumferential direction. Around the tip end of the respective trunnions 18, rollers 19 are rotatably supported through a needle bearing 10, while allowing the rollers to be displaced in the axial direction by certain distances. A tripod type constant velocity joint 10 is provided by engaging the respective rollers 19 with the respective guide grooves 16 on an inner face of the housing 13. The respective pairs of side faces 11, on which each of the above guide grooves 16 is provided, are formed to circular recesses. Accordingly, each of the rollers 9 is rotatably and pivotably supported between the respective pairs of the side faces 11.
When the constant velocity joint 10 as described above is used, for example, the first rotational shaft 12 is rotated. The rotational force of the first rotational shaft 12 is, from the housing 13, through the roller 19, the needle bearing 20 and the trunnion 18, transmitted to the boss 17 of the tripod 15, thereby rotating the second rotational shaft 14. Further, if a central axis of the first rotational shaft 12 is not aligned with that of the second rotational shaft 14 (namely, a joint angle is not zero in the constant velocity joint 10), each of the trunnion 18 displaces relative to the side face 16a of each of the guide groove 16 to move around the tripod 15, as shown in FIGS. 18 and 19. At this time, the rollers 19 supported at the ends of the trunnions 18 move along the axial directions of the trunnions 18, respectively, while rolling on the side faces 16a of the guide grooves 16, respectively. Such movements ensure that a constant velocity between the first and second rotational shafts 12 and 14 is achieved.
If the first and second rotational shafts 12 and 14 are rotated with the joint angle present, in the case of the constant velocity joint 10 which is constructed and operated as described above, each of the rollers 19 moves with complexity. For example, each of the rollers 19 moves in the rotational axis 12 of the housing 13 along each of the side faces 16a of the respective guide grooves 16, while the orientations of the rollers 19 are being changed and further the rollers 19 displace in the axial direction of the trunnion 18. Such complex movements of the rollers 19 cannot cause a relative movement between a peripheral outside face of each of the rollers 19 and each of the side faces 16a of the guide grooves 16 to be smoothly effected. Thus, a relatively large friction occurs between the faces. As a result, in the constant velocity joint 10, three-directional axial forces occurs per one rotation. It is known that an adverse oscillation referred to as xe2x80x9cshudderxe2x80x9d may occur in some cases, if a large torque is transmitted with a relatively large joint angle present.
In order to solve the above problem, FR275280 discloses a structure as shown in FIG. 20 and the Japanese Laid-Open patent application No. H3-172619 discloses a structure as shown in FIG. 21. In the structure shown in FIG. 20, a roller is guided parallel to a housing groove and a spherical trunnion 18 can swing and pivot around a inner spherical surface of an inner roller 19b. Further, a contact area between the inner spherical surface of the inner roller 19b and the trunnion 18 when receiving a torque for a load is shaped to an ellipse having a larger long diameter, because a radius xe2x80x9crxe2x80x9d of a longitudinal cross-sectional shape of the spherical trunnion 18 is smaller than a radius xe2x80x9cr3xe2x80x9d of the trunnion 18. In the structure shown in FIG. 21, a torque for a load is received between an inner cylindrical surface of an inner roller 19b and a spherical trunnion 18. Thus, a width (a short diameter) xe2x80x9cbxe2x80x9d of a contact ellipse shaped therebetween is smaller and a contact length xe2x80x9caxe2x80x9d, in the circumference of a contact area, which corresponds to a long diameter of the contact ellipse is larger. In fact, the contact ellipse is positioned on the side of the trunnion 18 facing with the side face 16a of the guide groove 16, although the contact ellipse is shown at the front side for clarification in FIG. 21. When these joints rotate with joint angles present upon receiving loads, as shown in FIG. 22, a pivotal movement (of a direction indicated by an arrow xe2x80x9cHxe2x80x9d) of the trunnion 18 causes a pivotal sliding action to be occurred on the contact ellipse. Then the pivotal sliding action operates as a spin moment (of a rotational direction indicated by arrows xe2x80x9cBxe2x80x9d) so as to change a rolling direction of the roller assembly 19 comprising the inner roller 19b and the outer roller 19a, which are assembled together via a needle bearing 21. As a result, the direction of the roller assembly 19 is changed until it is in contact with inner or outer face of the guide groove 16, and in addition a contact force is increased. Moreover, the roller assembly 19 displaces not to be parallel to the guide groove 16. Hence, it is difficult for the roller assembly 19 to be smoothly rolled, bringing about a significant rolling resistance.
It is contemplated to enlarge a difference between an inner diameter of the inner roller 19b and an outer diameter of the trunnion 18, in order to reduce the long diameter xe2x80x9caxe2x80x9d of the contact ellipse. In this case, however, there is raised a new problem in which the joint fluctuates when moving along the rotational direction.
The object of the present invention is to overcome the above disadvantages of prior art, that is, to provide a tripod type constant velocity joint having a simple structure which is both highly strong and durable, which can diminish a spin moment acting on the contact ellipse formed between the outer face of the trunnion and the inner face of the inner roller, due to the pivotal sliding movement of the trunnion axis, and which can minimize a rolling resistance when rotating with any joint angle present.
To solve the above problems, according to the invention, a constant velocity joint of tripod type comprises:
A cylindrical hollow housing defining an opening at one end, and being secured at its opposite end to a first rotating shaft such that a central axis of the housing is aligned with that of the first rotating shaft, an inner face of the housing being provided with three guide grooves extending in a axial direction of the housing and being spaced apart equally in a circumferential direction, each groove having a pair of side faces opposed to each other, extending in the axial direction, and a bottom portion connecting between the side faces; and
A tripod provided at an angle normal to a second rotating shaft and secured to one end of the second rotating shaft, the tripod having three trunnions positioned in the grooves, the trunnions being spaced apart equally in a circumferential direction and securing equally to the second rotating shaft at an angle normal, with respective inner rollers being mounted to outside end portions of respective trunnions, and with respective outer rollers being mounted on the outer faces of inner rollers through a needle bearing, the outer faces of the outer rollers being shaped so as to allow movement only in an axial direction of the guide grooves, the side faces receiving a load, and a part of the bottom portion guiding the rolling of the outer roller.
The constant velocity joint of tripod type is characterized in that, the inner rollers have a spherical inner circumferential surface, respectively; and
The trunnions have a elliptical shape in the sectional view normal to each of their axes, respectively and is positioned so that the short diameter of the ellipse is substantially parallel to the second rotating shaft.
According to the invention as constructed above, elliptical contact areas formed in transmitting torque between the inner spherical face of the inner roller and the outer face of the generally spherical trunnion can be maintained relatively small without significant fluctuations during rotating. Thus, it is possible to diminish a spin moment acting on the contact ellipse due to the pivotal sliding movement of the trunnion axis. Accordingly, the invention can bring about advantages including a relatively small contact force between the outer roller and the guide groove, a stable rolling of the outer roller, a smaller rolling resistance and a lower axial force of the joint.
These and other objects and advantages of the present invention will be more apparent from the following detailed description and drawings in which: